It is known to use optical high-power transmitters for optical free-space transfer between satellites. A transmission system known per se for optical transfer of data between satellites is depicted in FIG. 1. In this, a laser oscillator 1 supplies an optical signal of constant power and frequency with a narrow spectral width. The subsequent electrooptical modulator 2 impresses the data information onto the signal. Modulation for impressing the data to be transferred onto the optical signal can be accomplished either by amplitude modulation or by way of one of the various phase modulation systems (PSK).
The optical signal generated in this fashion is conveyed to a first optical preamplifier 3. In preamplifier 3, embodied as a fiber amplifier, the optical power of the signal is elevated to a level of, typically, one watt. By way of a downstream crystal amplifier 4, the optical signal is amplified to a high optical level necessary for transfer. The power section of the amplifier chain is embodied in fiber-coupled fashion in order to convey the beams, by way of fiber 5, over a greater distance to the remote optical unit. From laser oscillator 1 and as far as collimator 6, the optical signal is guided in a fiber 5. All fibers 5 in the system are polarization-retaining. The optical beam is conveyed via collimator 6, via an optional transit/receive splitter 7 and displacement mirror 8 for beam alignment, to mirror telescope 9, and from there to the counterpart station.
A disadvantage of this apparatus for optical transfer of data is that for systems with a very high transmitting power, the demands in terms of signal separation between the transmit and receive paths become so great that they can no longer be met within a shared optical path. It is then necessary to separate the two paths completely, i.e. to use a separate telescope 9 for transmitter and receiver. Although transmit/receive splitter 7 is omitted in such a case, the use of an additional mirror telescope 9 nevertheless causes overall costs for the system to rise considerably.